Balloons are routinely used to resolve or address flow restrictions or perhaps even complete blockages in tubular areas of the body, such as arteries or veins. In many clinical situations, the restrictions are caused by hard solids, such as calcified plaque, and require the use of high pressures to compact such blockages. Commercially available balloons employ complex technology to achieve high pressure requirements without sacrificing the profile of the balloon. Besides high pressure requirements, the balloons should also be resistant to puncture, easy to track and push, and present a low profile, especially when used for angioplasty.
In clinical practice, angioplasty balloons are expanded from a deflated, folded state to an expanded state within a vessel to treat a target area, such as a portion of the circumferential inner wall 1 of a blood vessel V, as shown in FIGS. 1 and 2. The inflation is traditionally completed using an X-ray contrast agent to provide better visibility under X-ray or other form of radiography during the interventional procedure, as illustrated in FIGS. 3 and 4 (note contrast media CM having a width DX within the wall 28 of balloon 12, which is bombarded with radiation R). Typically, a 70/30 percent mixture of contrast agent and saline is used to inflate the balloon during an angioplasty procedure.
The physician performing the angioplasty procedure should be able to locate the position of the uninflated balloon with accuracy, so that the balloon will be properly positioned once inflated. This is conventionally accomplished by attaching marker bands on the catheter shaft in the region corresponding to the balloon working surface. This “working surface” is the surface along the portion of the balloon that is used to achieve the desired treatment effect, such as contacting the calcified plaque (which surface in the case of a balloon having conical or tapering sections at the proximal and distal ends is typically co-extensive with a generally cylindrical barrel section).
Misalignment of the marker bands during placement along the shaft sometimes results in their failure to correspond precisely to the extent of the working surface, as is shown in FIG. 5 (note misalignment amount X between each interior marker band M carried by shaft S and working surface W of balloon 12, which also typically includes a radiopaque tip P at the distal end). Even upon exercising great care to position the markers properly on the underlying shaft in alignment with anticipated boundaries of the working surface when the balloon is inflated, there remains a tendency for mismatch due to several possible factors. One such factor may be the tolerance stack-ups arising as a consequence of the affixation of the balloon to the distal end of the catheter shaft. The balloon also has a tendency to grow in the longitudinal direction when inflated, especially with large and particularly long balloons. Another factor is the tendency of the portion of the catheter shaft within the balloon to bend or flex during inflation. This may lead to misalignment between radiopaque markers fixed to the shaft and the working surface.
Whatever the cause, the resulting misalignment may prevent the clinician from accurately identifying the location of the working surface of the balloon during an interventional procedure. This may lead to a geographic misplacement, or “miss,” of the intended contact between the target area T and the working surface W of the balloon 12 (see FIG. 2). It is especially desirable to avoid such an outcome when the balloon is designed to deliver a payload (such as a drug, stent, or both) or a working element to a specified location within the vasculature, since a miss may prolong the procedure (such as, for example, by requiring redeployment of the balloon 12 or the use of another balloon catheter in the case of a drug coated balloon).
During inflation and deflation of the balloon, it is desirable to avoid certain outcomes. On inflation, the application of pressure to the balloon via the contrast agent may cause the balloon to lengthen in a differential manner and thus take on a curved, banana-like shape. This curvature can lead to misalignment of the working surface of the balloon with reference points, such as radiopaque markings provided on an underlying catheter shaft, or the targeted treatment area. This may lead to a geographic misplacement, or “miss,” of the intended contact between the target area and the working surface of the balloon. It is especially desirable to avoid such an outcome when the balloon is designed to deliver a payload (such as a drug, stent, or both) or a working element to a specified location within the vasculature, since a miss may prolong the procedure (such as, for example, by requiring redeployment of the balloon 12 or the use of another balloon catheter in the case of a drug coated balloon).
Upon deflation, the balloon may also be subject to a phenomenon known as “pancaking.” In this condition, the balloon 12 folds down upon itself to a flattened state. This situation may cause the balloon to be viewed through fluoroscopy as perhaps still being in the inflated condition, since the full width of the balloon may still be perceived. This can give the clinician the false perception that the balloon remains inflated, when in fact it is not.
Accordingly, the need is identified for a balloon catheter that helps to avoid the foregoing problems associated with excessive curvature on inflation, pancaking on deflation, and others